1. Field of the Invention
The present invention relates to a data recovery apparatus and method, and more particularly, to a data recovery apparatus and method used in a receiving device.
2. Description of the Prior Art
Generally speaking, be it a wired or wireless system, during transmission the quality of signals is always subject to influences of the transmission medium, temperature, or electromagnetic interferences, leading to signal amplitude attenuations or waveform distortions. In order for the receiving end to observe a signal transmitted via the transmission channel or medium, that is substantially the same as the signal transmitted at the transmitting end, the receiver of an electronic device usually features a data recovery circuit to recover the received signal. A typical data recovery circuit includes an equalizer for equalizing the received signal in order to impose different gain values upon the various frequency bands of the signal, and an over-sampling circuit for over-sampling the equalized signal. Because transmission channels/media vary according to surroundings, an adaptive equalizer is used to dynamically adjust its equalization process according to changes in transmission channels and media.
Considering an example where over-sampling with doubled sampling frequency is performed, please refer to FIGS. 1A to 1D of schematic diagrams showing how the adaptive equalizer adjusts its parameters. FIGS. 1A and 1B illustrate the sampling operation when the received and equalized signal transits from low level (0) to high level (1), while FIGS. 1C and 1D illustrate the sampling operation when the received and equalized signal transits from high level (1) to low level (0). In the example shown in FIGS. 1A and 1B, being under doubled sampling frequency, there are sampling points, such as the second and fourth sampling points, falling upon the center portion of the signal, while there are also sampling points, such as the third sampling point, falling at the edge of the signal. Those falling on the center portion of the signal are used for determining received data value, and those falling at the edge of the signal are used for determining whether the parameters of the equalizer are appropriately set or not. For example, in FIG. 1A the sampling point on the edge of the signal determines that the received signal is at the low level (0), indicating that the transition of the signal level is too slow, and an adjustment to the parameters of the equalizer is necessary so as to increase its high-frequency gain and therefore to make the transition of the signal at this sampling point take place earlier. Conversely, in FIG. 1B the sampling point on the edge of the signal determines that the received signal is at the high level (1), indicating that the transition of the signal is too fast, and the parameters of the equalizer should be adjusted so as to reduce the high-frequency gain and to have the transition of the signal at this sampling point take place later. In the case of transitions from the high to the low level shown in FIGS. 1C and 1D, similar observation can be made and the aforementioned parameter adjusting rule for the equalizer also applies.
Please refer to FIGS. 2A and 2B of schematic diagrams, similarly showing over-sampling of the equalized signal transiting from low level (0) to high level (1). The difference between FIGS. 2A and B and FIGS. 1A to 1D is that the initial configuration of the equalizer in FIG. 2A is with an overly strong high frequency gain. As the result, a bouncing 10′ in FIG. 2A may occur at the region of signal transition. If such bouncing is so significant that the value sampled at the edge of the signal is likely to be determined as low level (0), as shown in FIG. 2A, applying the equalizer parameter adjustment algorithm as explained above, an even larger high-frequency gain would result, causing an even more significant bouncing phenomenon as shown in FIG. 2B. In this case, a positive feedback in an erroneous direction is formed, rendering the data recovery process impossible to properly operate.